U.S. patent application number 16/546872 was filed with the patent office on 2019-12-12 for depolarizing film, depolarizing member, and method for producing depolarizing film.
This patent application is currently assigned to FUJIFILM Corporation. The applicant listed for this patent is FUJIFILM Corporation. Invention is credited to Hideki KANEIWA, Daisuke KASHIWAGI, Ayako MURAMATSU, Yukito SAITOH, Yujiro YANAI.
Application Number | 20190377117 16/546872 |
Document ID | / |
Family ID | 63253036 |
Filed Date | 2019-12-12 |
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United States Patent
Application |
20190377117 |
Kind Code |
A1 |
SAITOH; Yukito ; et
al. |
December 12, 2019 |
DEPOLARIZING FILM, DEPOLARIZING MEMBER, AND METHOD FOR PRODUCING
DEPOLARIZING FILM
Abstract
Provided is a depolarizing film including a depolarizing layer
composed of a first region and a second region having differing
optical characteristics, wherein in the depolarizing layer, the
ratio between the area of the first region and the area of the
second region is 0.45:0.55 to 0.55:0.45, the first region is an
optically anisotropic region causing 90.degree. optical rotation of
light that is incident on one surface of the depolarizing layer
before the light is emitted from the other surface, and the second
region is an optically isotropic region having optical
isotropy.
Inventors: |
SAITOH; Yukito; (Kanagawa,
JP) ; KASHIWAGI; Daisuke; (Kanagawa, JP) ;
MURAMATSU; Ayako; (Kanagawa, JP) ; YANAI; Yujiro;
(Kanagawa, JP) ; KANEIWA; Hideki; (Kanagawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
FUJIFILM Corporation
Tokyo
JP
|
Family ID: |
63253036 |
Appl. No.: |
16/546872 |
Filed: |
August 21, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2018/000513 |
Jan 11, 2018 |
|
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16546872 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B05D 7/00 20130101; B05D
3/06 20130101; B05D 7/24 20130101; B05D 5/06 20130101; B05D 1/36
20130101; G02F 1/133502 20130101; G02B 27/286 20130101; G02B 5/3016
20130101 |
International
Class: |
G02B 5/30 20060101
G02B005/30 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2017 |
JP |
2017-033681 |
Claims
1. A depolarizing member including two depolarizing films and a
.lamda./4 plate, the depolarizing films being disposed such that
respective depolarizing layers thereof face each other, with the
.lamda./4 plate interposed therebetween, wherein: each depolarizing
film includes a depolarizing layer comprising a first region and a
second region having differing optical characteristics, in each
depolarizing layer, a ratio between an area of the first region and
an area of the second region is 0.45:0.55 to 0.55:0.45, the first
region is an optically anisotropic region causing 90.degree.
optical rotation of light that is incident on one surface of the
depolarizing layer and is emitted from another surface, and the
second region is an optically isotropic region having optical
isotropy.
2. The depolarizing member according to claim 1, wherein the first
region is formed by immobilizing a liquid crystalline phase that is
oriented with a 90.degree. twist between the one surface and the
other surface of the depolarizing layer.
3. The depolarizing member according to claim 2, wherein the second
region is formed from an isotropic phase formed by the same liquid
crystal material as the liquid crystal material that constitutes
the first region.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of
International Application No. PCT/JP2018/000513, filed Jan. 11,
2018, the disclosure of which is incorporated herein by reference
in its entirety. Further, this application claims priority from
Japanese Patent Application No. 2017-033681, filed Feb. 24, 2017,
the disclosure of which is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to a depolarizing film that
eliminates polarizability of an incident ray of light, a
depolarizing member, and a method for producing a depolarizing
film.
2. Description of the Related Art
[0003] For the purpose of suppressing coloration that makes the
polarization of a display surface polarizing plate isotropic,
eliminating the polarization-dependency of a sensor, reducing
speckle noise in an image projection device that projects an image
on a screen using laser light, or the like, depolarizing elements
are used. In regard to conventional depolarizing elements, as a
method for depolarization of the elements, a method of disposing a
plurality of birefringent materials in a plane such that the slow
axes are oriented in a plurality of directions is generally
used.
[0004] For example, in JP2006-47421A, a depolarizing element having
a stripe-shaped or checker-shaped planar pattern in which a region
provided with a 1/2 wavelength plate (.lamda./2 plate) and a region
provided with a simple transmission member that does not give a
phase difference are alternately disposed in a plane of light
incidence for the purpose of reducing speckle noise is
disclosed.
[0005] However, in the case of a configuration including a first
region and a second region as described above, in a case in which
the inclination between the optical axis (slow axis) of the
.lamda./2 plate and the polarizing axis of incident linearly
polarized light is 45.degree. (or -45), an effect of depolarization
can be obtained. However, in a case in which the polarizing axis of
incident light is not 45.degree. (or -45.degree.), there is a
problem that an effect of depolarization does not occur.
[0006] Furthermore, according to the depolarizing element of
JP2006-47421A, in view of the characteristics of the .lamda./2
plate, there is a problem that high depolarizability can be
obtained only at particular wavelengths.
[0007] As a configuration that solves this problem and enables
realization of depolarization for light in a wide range of
wavelength, or depolarization irrespective of the direction of the
polarizing axis of incident linearly polarized light, a
depolarizing element having a configuration in which a first
birefringent material layer and a second birefringent medium layer
are laminated, and two birefringent medium layers each include two
or more regions having different directions of the fast axis, has
been suggested in JP2013-130810A.
SUMMARY OF THE INVENTION
[0008] However, as in the case of the depolarizing element of
JP2013-130810A, in order to form regions having different
directions of the fast axis within one layer, complicated control
of orientation is required, and therefore, there is a problem that
productivity may be low. Furthermore, since the direction of
orientation becomes unstable in a boundary region between regions
having different directions of the fast axis, there is a problem
that definition enhancement is difficult.
[0009] In view of such circumstances, it is an object in the
invention to provide a depolarizing film and a depolarizing member,
which enable satisfactory depolarization independently of the
wavelength of an incident ray or the direction of the polarizing
axis, and provide high productivity with a simple configuration. It
is another object in the invention to provide a production method
by which a depolarizing film capable of depolarization
independently of the wavelength of an incident ray can be produced
easily.
[0010] The depolarizing film in the invention is a depolarizing
film including a depolarizing layer composed of a first region and
a second region having differing optical characteristics, wherein a
ratio between the area of the first region and the area of the
second region in each depolarizing layer is 0.45:0.55 to 0.55:0.45,
the first region is an optically anisotropic region that causes
90.degree. optical rotation of light incident on one surface of the
depolarizing layer before the light is emitted from another
surface, and the second region is an optically isotropic region
having optical isotropy.
[0011] It is preferable for the depolarizing film in the invention
that the first region is formed by immobilizing a liquid
crystalline phase oriented with a 90.degree. twist between one
surface and the other surface of the depolarizing layer.
[0012] In regard to the depolarizing film in the invention, it is
preferable that in a case in which the first region is formed from
a liquid crystalline phase, the second region is formed from an
isotropic phase formed by the same liquid crystal material as the
liquid crystal material constituting the first region.
[0013] It is preferable that the depolarizing film in the invention
is formed by laminating a .lamda./4 plate on one surface or the
other surface of the depolarizing layer.
[0014] A depolarizing member in the invention includes a
depolarizing film including a depolarizing layer; and a
depolarizing film including a depolarizing layer and further
including a .lamda./4 plate, the two depolarizing films being
disposed such that the two depolarizing layers face each other with
the .lamda./4 plate interposed therebetween.
[0015] A method for producing a depolarizing film in the invention
comprises:
[0016] a coating step of evenly applying a polymerizable liquid
crystal composition including a polymerizable liquid crystal
compound having a cationic polymerizable group and a photoradical
polymerizable group, a chiral agent, and a cationic polymerization
initiator on a support and forming a coating film;
[0017] an aging step of orienting the liquid crystal compound into
a twisted liquid crystalline phase within the coating film;
[0018] an ultraviolet curing step including: a full-face exposure
step of irradiating the entire surface of the coating film after
the aging step with ultraviolet radiation, thereby causing a
photocationic polymerization reaction, and partially curing the
coating film to produce a semi-fixed liquid crystal film; an
initiator application step of applying an initiator supply solution
including a photoradical polymerization initiator on the surface of
the semi-fixed liquid crystal film; and a mask exposure step of
irradiating the semi-fixed liquid crystal film with ultraviolet
radiation through a mask having a non-opening part and an opening
part at an area ratio of 0.45:0.55 to 0.55:0.45 in a state in which
the mask is positioned on the semi-fixed liquid crystal film;
and
[0019] a heat treatment step of heat-treating the semi-fixed liquid
crystal film obtained after the ultraviolet curing step at a
temperature higher than or equal to the temperature of phase
transition to an isotropic phase,
[0020] wherein a depolarizing layer including a first region
corresponding to the opening part of the mask and a second region
corresponding to the non-opening part is formed.
[0021] In regard to the method for producing a depolarizing film in
the invention, it is preferable that the polymerizable liquid
crystal composition includes a polymerizable liquid crystal
compound represented by the following Formula (1):
Q-Sp.sup.1-L.sup.1-M.sup.1-L.sup.2-Sp.sup.2-Ox (1)
wherein in Formula (1), Q represents a polymerizable group; any one
of Sp.sup.1 and Sp.sup.2 represents a branched alkylene, or an
alkylene containing a divalent linking group selected from the
group consisting of --O--, and --S-- in at least one chain, while
the other represents a linear alkylene; L' and L.sup.2 each
independently represent a divalent linking group; M.sup.1
represents a mesogenic group having at least one divalent group
selected from the group consisting of groups represented by the
following Formulae (2-1) to (2-12); and Ox represents a group
represented by the following Formula (3):
##STR00001## ##STR00002##
[0022] in Formula (3), R.sup.2 represents a hydrogen atom, a methyl
group, or an ethyl group; X.sup.1 represents --O--, --S--, --OCO--,
or --COO--; X.sup.2 represents a single bond or an alkylene having
1 to 4 carbon atoms; and symbol * represents a site of bonding to
Sp.sup.2.
[0023] The depolarizing film in the invention is a depolarizing
film including a depolarizing layer composed of a first region and
a second region having differing optical characteristics, in which
the area ratio between the first region and the second region in
the depolarizing layer is 0.45:0.55 to 0.55:0.45, the first region
is an optically anisotropic region that causes 90.degree. optical
rotation of light incident on one surface of the depolarizing layer
before the light is emitted from the other surface, and the second
region is an optically isotropic region having optical isotropy.
Therefore, an emergent ray produced as light rays that have entered
the depolarizing film and passed through the first region and the
second region are mixed and depolarized, can be obtained. In the
present optically anisotropic region, since 90.degree. -rotation
can be achieved irrespective of the direction of the polarizing
axis, satisfactory depolarization is enabled without depending on
the direction of the polarizing axis. Furthermore, in a case in
which a .lamda./2 plate is used as in the case of conventional
configurations, there is a possibility that wavelength dispersion
may occur; however, in the present configuration, satisfactory
depolarization can be realized regardless of the wavelength.
Furthermore, since it is not a complicated structure in which
regions having different directions of the fast axis are formed
within one layer, the productivity is high, and definition
enhancement is also possible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a cross-sectional view and a plan view
schematically illustrating a depolarizing film of a first
embodiment.
[0025] FIG. 2 is a plan view illustrating another example of the
disposition pattern of first and second regions of a depolarizing
layer (No. 1).
[0026] FIG. 3 is a plan view illustrating another example of the
disposition pattern of the first and second regions of the
depolarizing layer (No. 2).
[0027] FIG. 4 is a plan view illustrating another example of the
disposition pattern of the first and second regions of the
depolarizing layer (No. 3).
[0028] FIG. 5 is a plan view illustrating another example of the
disposition pattern of the first and second regions of the
depolarizing layer (No. 4).
[0029] FIG. 6 is a schematic diagram for explaining the principle
for depolarization by the depolarizing film of the first
embodiment.
[0030] FIG. 7 is a cross-sectional view schematically illustrating
a depolarizing film of a second embodiment.
[0031] FIG. 8 is a schematic diagram for explaining the principle
for depolarization by the depolarizing film of the second
embodiment.
[0032] FIG. 9 is a cross-sectional view schematically illustrating
a depolarizing member of embodiments.
[0033] FIG. 10 is a schematic diagram for explaining the principle
for depolarization by the depolarizing member.
[0034] FIG. 11 is a flow chart showing a process for forming a
depolarizing layer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] In the following description, embodiments of the first
depolarizing film in the invention will be described with reference
to the drawings. In the respective drawings, the scale of the
constituent elements is made appropriately different from the
actual scale in order to make the constituent elements easily
recognizable.
[0036] <Depolarizing Film>
[0037] FIG. 1 is a schematic diagram illustrating a cross-sectional
view and a plan view of the depolarizing film 1 according to a
first embodiment in the invention.
[0038] The depolarizing film 1 according to the present embodiment
includes a depolarizing layer 20 on a support 10. The depolarizing
film in the invention may be composed only of a depolarizing
layer.
[0039] The depolarizing layer 20 has a first region 21 and a second
region 22 having differing optical characteristics. In the plan
view of FIG. 1, the first region 21 is shown in gray (similarly
applicable to FIG. 2 to FIG. 5 that will be described below) in
order to distinguish the first region 21 from the second region 22.
The area ratio S.sub.1:S.sub.2 between the area S.sub.1 of the
first region 21 and the area S.sub.2 of the second region 22 is
0.45:0.55 to 0.55:0.45. Here, the area S.sub.1 of the first region
21 and the area S.sub.2 of the second region 22 are defined as
total areas in a case in which the respective regions are present
in large numbers. According to the present embodiment, the first
region 21 and the second region 22 have an identical stripe shape
and are alternately disposed in the width direction at a period P
of, for example, 0.5 .mu.m to 2.0 .mu.m. In FIG. 1, the width
w.sub.1 in the direction of arrangement of the first region 21 and
the width w.sub.2 in the direction of arrangement of the second
region 22 are the same and are each a half of the period of
disposition P (w.sub.1=w.sub.2=P/2).
[0040] The phrase that the area S.sub.1:S.sub.2 is in the range of
0.45:0.55 to 0.55:0.45 implies that the area S.sub.1 and the area
S.sub.2 are almost equal. In a case in which the area ratio
S.sub.1:S.sub.2 is 0.45:0.55 to 0.55:0.45, the disposition is not
limited to the pattern of alternate disposition as shown in FIG. 1,
and the first region 21 and the second region 22 may be disposed in
any pattern.
[0041] The area of the first region and the area of the second
region can be determined by measuring the longitudinal and
transverse lengths of a region by measurement using an electron
microscope, and calculating the area.
[0042] The first region 21 is an optically anisotropic region
having a function of causing 90.degree. optical rotation of light
incident on one surface 20a of the depolarizing layer 20 before the
light is emitted from the other surface 20b. Light entering the
first region 21 is outputted in a state in which the electric field
vector is rotated 90.degree.. Therefore, in a case in which an
incident ray is linearly polarized light, the emergent ray has a
polarizing axis that forms an inclination of 90.degree. with
respect to the polarizing axis at the time of incidence,
irrespective of the direction of the polarizing axis of the
incident ray. On the other hand, in a case in which an incident ray
is circularly polarized light or non-polarized light, even if the
electric field vector is rotated 90.degree., the apparent
polarization state does not change, and the emergent ray has a
polarization state equivalent to that of the incident ray.
[0043] The phrase "having a function of causing 90.degree. optical
rotation of light" as used in the invention provides an effect of
rotating the electric field vector of an incident ray by 90.degree.
irrespective of the polarization state of the incident ray.
Providing an effect of rotating the polarizing axis 90.degree. only
for polarized light having its polarizing axis inclined at a
particular angle such as 45.degree. (or (-45.degree.) with respect
to the optical axis, as in the case of a .lamda./2 plate, does not
correspond to the effect of "having a function of causing
90.degree. optical rotation of light" in the invention.
[0044] Regarding the first region 21, the constituent material is
not limited as long as the region has a function of causing
90.degree. optical rotation of an incident ray and emitting the
incident ray; however, the first region 21 can be formed using, for
example, a liquid crystal material (polymerizable liquid crystal
composition). Specifically, in a liquid crystal layer, the first
region 21 can be constructed from a region formed by immobilizing a
liquid crystalline phase oriented with a 90.degree. twist
(90.degree. twisted liquid crystalline phase) between one surface
and the other surface of a liquid crystal layer. Generally, in
order to cause a 90.degree. twist, Gooch-Tarry conditions are
known, and a liquid crystal material satisfying these conditions
can be used. Specifically, the conditions are described in detail
in a book published by John Wiley & Sons, Inc.: Fundamentals of
Liquid Crystal Devices, written by: Shin-TsonWu, Deng-Ke Yang (see
the following Reference Document 1), page 201. Furthermore, Mauguin
conditions in which the pitch of twist is sufficiently large with
respect to the length are also known, and a liquid crystal material
satisfying these conditions can be used. Specifically, the
conditions are described in detail on page 64 of Reference Document
1 described above.
[0045] The second region 22 is an optically isotropic region having
optical isotropy. Therefore, the second region 22 does not affect
the polarization state of transmitted light and emits an incident
ray without changing the characteristics thereof. Regarding the
second region 22, the constituent material is not particularly
limited as long as it is optically isotropic, and the second region
may be even an air layer. In a case in which the first region 21 is
formed from the 90.degree. twisted liquid crystalline phase
described above, it is preferable that the second region 22 is
configured to have an isotropic phase formed by the same liquid
crystal material as the constituent material of the first region
21.
[0046] Whether the first region in the depolarizing layer has a
function of 90.degree. optical rotation and the second region has
isotropy can be checked by a known method such as, for example,
making measurement using an AxoStep High-Precision Mueller Matrix
Imaging Polarimeter manufactured by Axometrics, Inc., or the
like.
[0047] As described previously, the first region 21 and the second
region 22 in the depolarizing layer of the depolarizing film in the
invention are such that as long as the areas of the two are
approximately equal, there are no limitations on the pattern of
disposition. FIG. 2 to FIG. 5 are schematic plan views illustrating
examples of the pattern of disposition of first regions 21 and
second regions 22 in the depolarizing layer.
[0048] As illustrated in FIG. 2, the first region 21 and the second
region 22 have an identical rectangular shape, and a pattern of
disposition in which the rectangular shapes are alternately
disposed longitudinally and transversely (directions of the arrows
x and y in the figure) can be adopted. The respective
rectangular-shaped regions 21 and 22 may have an oblong rectangular
shape (w.sub.1x, w.sub.1y, w.sub.2x, w.sub.2y), or may have a
square shape w.sub.1x=w.sub.1y, w.sub.2x=w.sub.2y).
[0049] As illustrated in FIG. 3, a pattern of disposition in which
first regions 21 are two-dimensionally periodically disposed within
a second region 22 may also be adopted. At this time, the second
region 22 is formed from one continuous region. The area S.sub.2 of
the second region 22 and the total area S.sub.1 of a plurality of
the first regions 21 are almost equal.
[0050] Furthermore, the disposition of the first region 21 and the
second region 22 is not limited to patterns in which the regions
have an identical shape and are periodically disposed as shown in
FIG. 1 to FIG. 3, and as shown in FIG. 4, first regions 21 having
different sizes may be randomly provided within a second region
22.
[0051] As long as the areas S.sub.1 and S.sub.2 of the first region
21 and the second region 22 in the incident region of light are
almost equal, there are no limitations on the shape and disposition
of the respective regions. The patterns of disposition shown in
FIG. 1 to FIG. 4 are such that both or one of the first region 21
and the second region 22 is formed from a plurality of regions;
however, it is also acceptable that both the regions are formed
from only one region as shown in FIG. 5.
[0052] In the present depolarizing film 1, light entering the first
region 21 of the depolarizing layer 20 undergoes 90.degree. optical
rotation and is emitted, and light entering the second region 22 is
emitted while maintaining the polarization characteristics at the
time of incidence. As described previously, in a case in which the
areas of the first region 21 and the second region 22 in the
depolarizing film 1 have equal areas, approximately half the
quantity of the light incident on the depolarizing film 1 passes
through the first region 21, undergoes 90.degree. optical rotation,
and is emitted, while the remaining approximately half the quantity
passes through the second region 22 and is emitted while
maintaining the polarization characteristics at the time of
incidence. As the two regions are equal, and rays that have added
the two regions are mixed (synthesized), the emergent ray becomes
depolarized light. That is, linearly polarized light incident on
one surface 1a of the depolarizing film 1 is emitted from the other
surface 1b as depolarized light. Meanwhile, the depolarizing film 1
is such that even in a case in which linearly polarized light is
made incident on the other surface 1b and is emitted from the one
surface la, the effect of depolarization can be similarly obtained.
It is because the principle is similar while simply the direction
of optical rotation of light in the first region 21 is
reversed.
[0053] The principle of depolarization by the present depolarizing
film 1 will be explained in more detail with reference to FIG. 6.
FIG. 6 is a schematic diagram for explaining the principle for
depolarization of linearly polarized light. In FIG. 6, in regard to
a case in which the incident ray is linearly polarized light, and
the inclination of the polarizing axis with respect to the +x-axis
in the plane of the depolarizing film 1 (xy plane) is 0.degree.
(P.sub.0), 90.degree. (P.sub.90), 45.degree. (P.sub.45), and
135.degree. (P.sub.135), and in regard to a case in which the
incident ray is circularly polarized light and is left-handed
circularly polarized light (P.sub.L), the polarization states
before incidence on the depolarizing layer 20 and after emission
from the depolarizing layer 20 are shown. FIG. 6 shows the
polarization state of an incident ray at the time when light passes
through the depolarizing film 1 in the z-direction (FIG. 1), and
the polarization states before and after the passage. The
depolarizing layer 20 shows the xz cross-section, and the
polarization state shows polarized light in the xy plane. The same
also applies to FIG. 8 and FIG. 10 that will be described
below.
[0054] In a case in which the incident ray is linearly polarized
light and has a polarizing axis P.sub.0 along the x-axis (the
inclination with respect to the +x-axis is 0.degree.), the portion
of light that passes through the first region 21 in the incident
ray has its polarizing axis rotated by 90.degree. and is emitted as
linearly polarized light having a polarizing axis P.sub.90 inclined
by 90.degree. with respect to the +x-axis. On the other hand, the
portion of light that passes through the second region 22 is
emitted at an inclination of 0.degree. without having its
polarizing axis changed. Therefore, the light emitted from the
first region 21 and the light emitted from the second region have
polarizing axes P.sub.90 and P.sub.0 that orthogonally intersect
each other. As the areas of the first and second regions in the
depolarizing layer 20 are approximately equal, the rays that have
passed through the first and the second regions are mixed
(synthesized), and thereby an emergent ray having the linear
polarization eliminated can be obtained.
[0055] In a case in which the incident ray is linearly polarized
light and has a polarizing axis P.sub.90 inclined by 90.degree.
with respect to the +x-axis, the portion of light that has passed
through the first region 21 in the incident ray has its polarizing
axis rotated by 90.degree. and is emitted as linearly polarized
light having a polarizing axis P180 (=P.sub.0) inclined by
180.degree. (along the x-axis) with respect to the +x-axis.
Meanwhile, the portion of light that has passed through the second
region 22 is emitted at an inclination of 90.degree., without
having its polarizing axis changed. Therefore, the light emitted
from the first region 21 and the light emitted from the second
region 22 have polarizing axes P.sub.180 and P.sub.90 that
orthogonally intersect each other. At this time, as described
above, the rays that have passed through the first and second
regions are synthesized, and consequently, an emergent ray having
the linear polarization eliminated can be obtained.
[0056] In a case in which the incident ray is linearly polarized
light and has a polarizing axis P.sub.45 inclined at 45.degree.
with respect to the +x-axis, the portion of light that has passed
through the first region 21 in the incident ray has its polarizing
axis rotated by 90.degree. and is emitted as linearly polarized
light having a polarizing axis P.sub.135 inclined at 135.degree.
with respect to the +x-axis. Meanwhile, the portion of light that
has passed through the second region 22 is emitted at an
inclination of 45.degree. without having its polarizing axis
changed. Therefore, the light emitted from the first region 21 and
the light emitted from the second region have polarizing axes
P.sub.135 and P.sub.45 that orthogonally intersect each other. At
this time, as described above, the rays that have passed through
the first and second regions are synthesized, and consequently, an
emergent ray having the linear polarization eliminated can be
obtained.
[0057] Similarly, in a case in which the incident ray is linearly
polarized light and has a polarizing axis P.sub.135 inclined at
135.degree. with respect to the +x-axis, the portion of light that
has passed through the first region 21 in the incident ray has its
polarizing axis rotated at 90.degree. and is emitted as linearly
polarized light having a polarizing axis P.sub.225 (=P.sub.45)
inclined at 225.degree. with respect to the +x-axis.
[0058] Meanwhile, the portion of light that has passed through the
second region 22 is emitted at an inclination of 135.degree.
without having its polarizing axis changed. Therefore, the light
emitted from the first region 21 and the light emitted from the
second region 22 have polarizing axes P.sub.225 and P.sub.135 that
orthogonally intersect each other. At this time, as described
above, the rays that have passed through the first and second
regions are synthesized, and consequently, an emergent ray having
the linear polarization eliminated can be obtained.
[0059] In case in which the incident ray is linearly polarized
light, there are no limitations on the inclination .alpha. with
respect to the x-axis of the polarizing axis. The inclination of
the polarizing axis after the incident ray has passed through the
first region 21 is .alpha.+.pi./2, and the inclination .alpha. of
the polarizing axis of the light that has passed through the second
region 22 is maintained without change. Therefore, since the
polarizing axes of the light that has passed through the first
region 21 and the light that has passed through the second region
22 necessary orthogonally intersect each other, an emergent ray
having the polarization eliminated can be obtained regardless of
the inclination .alpha. of the polarizing axis of the incident
ray.
[0060] With the depolarizing film of the present configuration, a
similar effect of depolarization can be obtained at any wavelength
of incidence, regardless of the wavelength of the incident ray.
[0061] On the other hand, in a case in which the incident ray is
circularly polarized light and is left-handed circularly polarized
light P.sub.L, since the rays that have passed through the first
region 21 and the second region 22 are emitted while still being
left-handed circularly polarized light P.sub.L, the emergent ray
maintains the polarization state of the left-handed circularly
polarized light P.sub.L. Although not shown in the diagram, in a
case in which the incident ray is right-handed circularly polarized
light, similarly the emergent ray remains as right-handed
circularly polarized light.
[0062] FIG. 7 is a schematic cross-sectional view of a depolarizing
film 2 of a second embodiment.
[0063] The depolarizing film 2 of the second embodiment is formed
by a depolarizing layer 20 and a .lamda./4 plate 30 laminated
together.
[0064] The configuration of the depolarizing layer 20 is the same
as that of the depolarizing layer 20 in the depolarizing film of
the first embodiment. It is preferable from the viewpoint of
suppressing wavelength dispersion that the .lamda./4 plate 30 is a
broadband .lamda./4 plate that can give a constant phase difference
(.lamda./4) at any wavelength.
[0065] The depolarizing film 2 is to provide a depolarizing effect
for circularly polarized light incident on a surface 2a on the
.lamda./4 plate 30 side of the depolarizing film. The light
incident on the side of the .lamda./4 plate 30 of the depolarizing
film 2 passes through the .lamda./4 plate 30 and the depolarizing
layer 20 in order and is emitted from the other surface 2b. The
principle of depolarization will be explained with reference to
FIG. 8. FIG. 8 is a schematic diagram for explaining the principle
for depolarization of circularly polarized light by a depolarizing
film. In FIG. 8, in regard to a case in which the incident ray is
circularly polarized light and is left-handed circularly polarized
light (P.sub.L) or right-handed circularly polarized light
(P.sub.R), and a case in which the incident ray is linearly
polarized light and the inclination of the polarizing axis with
respect to the +x-axis in a plane (xy plane) of the depolarizing
film 2 is 0.degree. (polarizing axis P.sub.0), the polarization
states before incidence on the .lamda./4 plate 30 (before incidence
on film 2) and after passage through the 214 plate 30, and the
polarization state after passage through the depolarizing layer 20
(after emission from film 2) are respectively shown.
[0066] In a case in which the incident ray is circularly polarized
light and is left-handed circularly polarized light P.sub.L, light
that has passed through the 214 plate 30 is converted to linearly
polarized light. The polarizing axis of this linearly polarized
light is designated as the +x-axis. The portion of light that
passes through the first region 21 of the depolarizing layer 20 in
the light that has become linearly polarized by passing through the
.lamda./4 plate, has its polarizing axis rotated by 90.degree., and
the portion of light that passes through the second region 22 is
emitted directly without having the polarizing axis rotated.
Therefore, the polarizing axes of the light emitted from the first
region 21 of the depolarizing layer 20 and the light emitted from
the second region 22 orthogonally intersect each other. As a result
of the above-described action, circularly polarized light incident
on the surface 2a on the .lamda./4 plate 30 side of the
depolarizing film 2 is emitted from the surface 2b on the
depolarizing layer 20 side, as depolarized light.
[0067] Similarly, in a case in which the incident ray is circularly
polarized and is right-handed circularly polarized light P.sub.R,
the light that has passed through the .lamda./4 plate 30 is
converted to linearly polarized light. At this time, in a .lamda./4
plate 30 having an effect of converting left-handed circularly
polarized light P.sub.L into linearly polarized light having a
polarizing axis in the x-axis direction, right-handed circularly
polarized light P.sub.R is converted to linearly polarized light
having a polarizing axis in the y-axis direction that is inclined
by 90.degree. with respect to the x-axis. The portion of light that
passes through the first region 21 of the depolarizing layer 20 in
the light that has become linearly polarized light by passing
through the .lamda./4 plate, has its polarizing axis rotated by
90.degree., and the portion of light that passes through the second
region 22 is emitted directly. Thereby, the polarizing axes of the
light emitted from the first region 21 and the light emitted from
the second region 22 orthogonally intersect each other. Circularly
polarized light incident on the surface 2a on the .lamda./4 plate
30 side of the depolarizing film 2 is emitted from the surface 2b
on the depolarizing layer 20 side, as depolarized light.
[0068] On the other hand, in a case in which an incident ray is
linearly polarized light having a polarizing axis P.sub.0 in the
x-axis direction, light that has passed through the .lamda./4 plate
30 is converted to circularly polarized light in a predetermined
direction (in this case, left-handed). As described above, even if
the circularly polarized light passes through the depolarizing
layer 20, the polarization state is maintained without change.
Therefore, in a case in which linearly polarized light is made
incident on the present depolarizing film 2, linear polarization
itself is eliminated; however, circular polarization in a
predetermined direction remains in the emergent ray.
[0069] The depolarizing film 2 of the second embodiment may include
a support between the .lamda./4 plate 30 and the depolarizing layer
20, or on a surface of the depolarizing layer 20, the surface being
on the opposite side of the .lamda./4 plate 30.
[0070] As described above, the depolarizing film 1 of the first
embodiment provides an effect of depolarization for linearly
polarized light, and the depolarizing film 2 of the second
embodiment provides an effect of depolarization for circularly
polarized light. Thus, by combining the two, a depolarizing member
by which an effect of depolarization for both linearly polarized
light and circularly polarized light can be obtained, can be
constructed.
[0071] FIG. 9 is a schematic cross-sectional view of an embodiment
of the depolarizing member in the invention. The depolarizing
member 5 of the present embodiment is configured such that two
layers of depolarizing layers 120 and 220 are disposed to face each
other with a .lamda./4 plate 30 interposed therebetween.
[0072] The first and second depolarizing layers 120 and 220 both
have a configuration similar to that of the depolarizing layer 20
according to the first embodiment. In FIG. 9, the first
depolarizing layer 120 and the second depolarizing layer 220 are
disposed such that the respective first regions 121 and 221 and the
respective second regions 122 and 222 fall in line with each other;
however, the respective regions may be out of alignment.
Furthermore, the pattern of disposition of the first region 121 and
the second region 122 in the first depolarizing layer 120 may
differ from the pattern of disposition of the first region 221 and
the second region 222 in the second depolarizing layer 220. For
example, the first depolarizing layer 120 may have a checker-shaped
pattern as shown in FIG. 2, and the second depolarizing layer 220
may have a pattern in which first regions of various sizes are
randomly disposed as shown in FIG. 4. It is also preferable that
the .lamda./4 plate 30 is a broadband .lamda./4 plate, similarly to
the case of the depolarizing film 2 of the second embodiment.
[0073] The depolarizing member 5 of the present embodiment can give
a depolarization effect irrespective of whether the incident ray is
linearly polarized light or circularly polarized light. Light
incident on one surface 5a of the depolarizing member 5 passes
through a first depolarizing layer 120, a .lamda./4 plate 30, and a
second depolarizing layer 220 and is emitted from the other surface
5b. Meanwhile, similar effects can be obtained irrespective of
whether the incident ray is made incident on any of the surfaces 5a
and 5b.
[0074] The principle for depolarization by the depolarizing member
5 will be explained with reference to FIG. 10. FIG. 10 is a
schematic diagram for explaining the principle for depolarizing of
linearly polarized light and circularly polarized light by the
depolarizing member 5. In FIG. 10, in regard to a case in which the
incident ray is linearly polarized light, and the inclination of
the polarizing axis with respect to the +x-axis in a plane (xy
plane) of the depolarizing member 5 is 0.degree. (polarizing axis
P.sub.0), 90.degree. (polarizing axis P.sub.90), 45.degree.
(polarizing axis P.sub.45), and 135.degree. (polarizing axis
P.sub.135), and a case in which the incident ray is circularly
polarized light is left-handed circularly polarized light P.sub.L
or right-handed circularly polarized light P.sub.R, the
polarization states of before incidence on the first polarizing
layer 120 (before incidence on the depolarizing member 5), after
being transmitted through the first polarizing layer 120, after
being transmitted through the 214 plate 30, and after being
transmitted through the second depolarizing layer 220 (after
emission into the depolarizing member 5) are respectively
shown.
[0075] In a case in which the incident ray is linearly polarized
light and has a polarizing axis P.sub.0 along the x-axis (the
inclination with respect to the +x-axis is (0.degree.), the light
that passes through the first region 121 of the first depolarizing
layer 120 has its polarizing axis rotated by 90.degree. and is
emitted as linearly polarized light having a polarizing axis
P.sub.90 inclined by 90.degree. with respect to the +x-axis.
Meanwhile, the light that passes through the second region 122 of
the first depolarizing layer 120 is emitted at an inclination of
0.degree. without any change in the polarizing axis. The light that
has passed through the first region 121 of the first depolarizing
layer 120 and the light that has passed through the second region
122 are subsequently converted to circularly polarized lights in
mutually opposite directions by passing through the .lamda./4 plate
30. Since circularly polarized light does not have any change in
the polarizing state in the second depolarizing layer 220, the
lights are emitted from the first region 221 and the second region
222 while remaining as circularly polarized lights in mutually
opposite directions. The areas of the first region and the second
region are approximately equal. Circularly polarized lights in
mutually opposite directions cancel each other by being mixed
(synthesized), circular polarization is eliminated, and thus an
emergent ray that is finally depolarized can be obtained.
[0076] In a case in which the incident ray is linearly polarized
light, light that has been depolarized by passing through the first
depolarizing layer 120, the .lamda./4 plate 30, and the second
depolarizing layer 220 can be obtained under a similar principle,
irrespective of the inclination of the polarizing axis of the
incident ray with respect to the x-axis.
[0077] In a case in which the incident ray is circularly polarized
light and is left-handed circularly polarized light P.sub.L, rays
of light that have passed through the first region 121 and the
second region 122 in the first depolarizing layer 120 are both
emitted as left-handed circularly polarized light P.sub.L.
Subsequently, the light rays pass through the .lamda./4 plate 30
and are converted to linearly polarized light. Furthermore, the
portion of light that passes through the first region 221 in the
second depolarizing layer 220 has its polarizing axis rotated by
90.degree., and the portion of light that passes through the second
region 222 is emitted directly. The polarizing axes of the light
emitted from the first region 221 and the light emitted from the
second region 222 orthogonally intersect each other, and
consequently, a depolarized emergent ray can be obtained.
[0078] Also in a case in which the incident ray is right-handed
circularly polarized light PR, similarly, light that has been
depolarized by passing through the first depolarizing layer 120,
the .lamda./4 plate 30, and the second depolarizing layer 220 can
be obtained under a similar principle.
[0079] The depolarizing member 5 is configured such that the first
depolarizing layer 120, the .lamda./4 plate 30, and the second
depolarizing layer 220 are laminated as shown in FIG. 9; however,
the depolarizing member may include a support between the
respective layers or on the surface of light incidence or
emergence, and may also have gaps between the respective
layers.
[0080] Next, with regard to a case in which the first region 21 and
the second region 22 of the depolarizing layer 20 are formed from
the same liquid crystal material, the material and the production
method will be explained.
[0081] (Liquid Crystal Material)
[0082] Regarding the liquid crystal material for forming the
depolarizing layer 20, a composition including a polymerizable
liquid crystal compound having a cationic polymerizable group and a
radical polymerizable group, a chiral agent, and a cationic
polymerization initiator is preferred. The wavelength
characteristics of the polymerizable liquid crystal compound may be
positively dispersible or negatively dispersible. The composition
may further include other components such as an orientation
controlling agent and an alignment aid. Particularly, a
polymerizable liquid crystal composition including the
polymerizable liquid crystal compound described in JP2008-127336A
can be suitably utilized.
[0083] --Polymerizable Liquid Crystal Compound--
[0084] Regarding the polymerizable liquid crystal compound having a
cationic polymerizable group and a radical polymerizable group, a
polymerizable liquid crystal compound represented by the following
Formula (1) is suitable.
Q-Sp.sup.1-L.sup.1-M.sup.1-L.sup.2-Sp.sup.2-Ox (1)
[0085] In Formula (1), Q represents a polymerizable group.
According to the present specification, regarding the polymerizable
group Q, in a case in which --CO--, --OCO--, --COO--, and the like
are bonded to a polymerizable double bond or the like, these
--CO--, --OCO--, --COO--, and the like are also included in the
polymerizable group. Here, the polymerizable group Q is a radical
polymerizable group. Since Ox that will be described in detail
later is a cationic polymerizable group, polymerization reactions
can be carried out under different conditions by adopting a radical
polymerizable group. The radical polymerizable group is preferably
a (meth)acryloyloxy group or a (meth)acryloyl, and more preferably
a (meth)acryloyloxy group.
[0086] In Formula (1), any one of Sp.sup.1 and Sp.sup.2 represents
a branched alkylene, or an alkylene containing a divalent linking
group selected from the group consisting of --O--, --C.ident.C--,
and --S-- in at least one chain, while the other represents a
linear alkylene. As such, as different structures, that is,
asymmetric structures, are adopted for Sp.sup.1 and Sp.sup.2, the
solubility in an organic solvent, particularly MEK or the like, is
enhanced. Between a branched alkylene group and an alkylene
containing a divalent linking group selected from the group
consisting of --O--, --C.ident.C--, and --S-- in at least one
chain, preferred is an alkylene group containing --O-- or
--C.ident.C-- in the chain; and more preferred is
--(CH.sub.2).sub.n1--X--(CH.sub.2).sub.n2--. Here, n1 and n2 each
independently represent an integer from 1 to 4, and preferably 1 or
2. --X-- represents --O-- or and preferably --O--. In a case in
which --X-- is --O--, it is preferable that n1 and n2 are both 2,
and in a case in which --X-- is it is preferable that n1 and n2 are
both 1. The number of carbon atoms of the branched alkylene
(including the number of carbon atoms of the branch chain) is
preferably 4 to 12, more preferably 4 to 8, and even more
preferably 4 to 6. The branch chain is preferably a methyl group or
an ethyl group, and more preferably a methyl group.
[0087] The number of carbon atoms of the other linear alkylene is
preferably 2 to 12, more preferably 4 to 8, and even more
preferably 4 to 6. There are no particular limitations on the
selection of which of a branched alkylene or an alkylene containing
a divalent linking group selected from the group consisting of
--O--, --C.ident.C--, and --S-- in at least one chain, and a linear
alkylene will be adopted for Sp.sup.1 or Sp.sup.2, and selection
can be made as appropriate according to the use application or the
method. In the invention, in order to first polymerize --Ox between
the polymerizable group Q and --Ox, it is preferable that Sp.sup.2
is a linear alkylene, and Sp.sup.1 is a branched alkylene or an
alkylene containing a divalent linking group selected from the
group consisting of --O--, --C.ident.C--, and --S-- in at least one
chain. As such, in a case in which polymerization is carried out
stepwise, since the second polymerization has lowered fluidity
compared to the first polymerization, the polymerization ratio
tends to be lowered. From this, in a case in which a spacer on the
polymerizable group that is polymerized in the first round is a
branched alkylene or an alkylene containing a divalent linking
group selected from the group consisting of --O--, --C.ident.C--,
or --S-- in at least one chain, mesogenic sites are likely to
thermally fluctuate, and as a result, heat resistance is
deteriorated. Thus, by adopting a linear alkylene as a spacer on
the side of the polymerizable group that is polymerized in the
first round, thermal fluctuation of mesogenic sites is suppressed,
and consequently heat resistance is improved.
[0088] In Formula (1), L.sup.1 and L.sup.2 each independently
represent a divalent linking group. As long as L.sup.1 and L.sup.2
each represent a group that links Sp.sup.1 with M.sup.1 and
Sp.sup.2 with M.sup.1, there are no particular limitations;
however, L.sup.1 and L.sup.2 are each preferably a single bond,
--O--, --S--, --OCO--, --COO--, --CO--, --CH.sub.2--, --CONH--, or
--NHCO--. L.sup.1 and L.sup.2 are each more preferably a single
bond, --O--, --S--, --OCO--, or --COO--; even more preferably a
single bond, --O--, or --CH.sub.2--; and most preferably --O--. It
is preferable that L.sup.1 and L.sup.2 are the same divalent
linking groups, and it is more preferable that L.sup.1 and L.sup.2
together represent --O--. According to the present specification,
in a case in which --O-- is directly bonded to M.sup.1, --O-- is
handled as L.sup.1 or L.sup.2 and is not intended to constitute
Sp.sup.1 or Sp.sup.2.
[0089] In Formula (1), M.sup.1 represents a mesogenic group having
at least one divalent group selected from the following Formulae
(2-1) to (2-12), preferably having three or more such divalent
groups, and more preferably three such divalent groups.
##STR00003## ##STR00004##
[0090] For example, the divalent group represented by Formula (2-1)
represents an unsubstituted 1,4-cyclohexylene group, and the
divalent group represented by Formula (2-2) represents an
unsubstituted 1,4-phenylene group.
[0091] In a case in which the mesogenic group represented by
M.sup.1 is composed of two or more of the above-mentioned groups,
the above-mentioned groups may be respectively linked by a linking
group selected from the group consisting of a single bond, an
acetylene group (--C.ident.C--), --N.dbd.N--, --N.dbd.CH--,
--C(CN).dbd.CH--, --CONHCONHCO--, --O--, --S--, --OCO--, --COO--,
--OCOO--, --CO--, --CH.sub.2--, --OCH.sub.2--, --CH.sub.2O--,
--CONH--, --NHCO--, --NHCOO--, and --OCONH--. Preferably, the
above-mentioned groups may be respectively linked by a linking
group selected from the group consisting of a single bond, an
acetylene group (--C.ident.C--), --OCO--, --COO--, --OCH.sub.2--,
--CH.sub.2O--, --N.dbd.N--, --N.dbd.CH--, --C(CN).dbd.CH--,
--CONH--, --NHCO--, and --CONHCONHCO--; and more preferably, the
above-mentioned groups may be respective linked by a linking group
selected from the group consisting of a single bond, an acetylene
group (--C.ident.C--), --OCO--, --COO--, --CONH--, and
--NHCO--.
[0092] In Formula (1) described above, Ox represents a group
represented by the following Formula (3):
##STR00005##
[0093] In Formula (3) described above, R.sup.2 represents a
hydrogen atom, a methyl group, or an ethyl group; preferably a
methyl group or an ethyl group; and more preferably a methyl group.
X.sup.1 represents --O--, --S--, --OCO--, or --COO--; preferably
--O-- or --OCO-- (the Ox side is O, and the Sp side is CO); and
more preferably --O--. X.sup.2 represents a single bond or an
alkylene having 1 to 4 carbon atoms; preferably an alkylene having
1 or 2 carbon atoms; and more preferably an alkylene having one
carbon atom (methylene). Symbol * represents a site of bonding to
Sp.sup.2.
[0094] Specific examples of the polymerizable liquid crystal
compound represented by Formula (1) are listed in JP2008-127336A,
and those can be used as appropriate. The concentration of the
polymerizable liquid crystal compound in the polymerizable liquid
crystal composition is preferably 30% by mass to 99.9% by mass,
more preferably 50% by mass to 99.9% by mass, and even more
preferably 70% by mass to 99.9% by mass, with respect to the total
mass of the composition.
[0095] --Chiral Agent (Optically Active Compound)--
[0096] A chiral agent has a function of inducing a twisted liquid
crystalline phase. The chiral agent is not particularly limited,
and any known compound (for example, described in Liquid Crystal
Device Handbook, Chapter 3, Section 4-3, Chiral Agents for TN and
STN, page 199, edited by Japan Society for the Promotion of
Science, 142nd Committee, 1989), and isosorbide and isomannide
derivatives can be used.
[0097] A chiral agent generally contains an asymmetric carbon atom;
however, an axially asymmetric compound or a planar asymmetric
compound can also be used as the chiral agent. Examples of the
axially asymmetric compound or the planar asymmetric compound
include binaphthyl, helicene, paracyclophane, and derivatives
thereof. The chiral agent may have a polymerizable group. In a case
in which both the chiral agent and the liquid crystal compound have
a polymerizable group, a polymer having a repeating unit derived
from a polymerizable liquid crystal compound and a repeating unit
derived from a chiral agent can be formed by a polymerization
reaction between the polymerizable chiral agent and the
polymerizable liquid crystal compound. In this embodiment, it is
preferable that the polymerizable group carried by the
polymerizable chiral agent is a group of the same kind as the
polymerizable group carried by the polymerizable liquid crystal
compound. Therefore, it is preferable that the polymerizable group
of the chiral agent is also an unsaturated polymerizable group, an
epoxy group, or an aziridinyl group; more preferably an unsaturated
polymerizable group; and particularly preferably an ethylenically
unsaturated polymerizable group.
[0098] The chiral agent may also be a liquid crystal compound.
[0099] The chiral agent may also have a photoisomerizable group.
The photoisomerizable group is preferably an isomerization site of
a compound exhibiting photochromic properties, or an azo, azoxy, or
cinnamoyl group. Regarding specific compounds, the compounds
described in JP2002-80478A, JP2002-80851A, JP2002-179668A,
JP2002-179669A, JP2002-179670A, JP2002-179681A, JP2002-179682A,
JP2002-338575A, JP2002-338668A, JP2003-313189A, and JP2003-313292A
can be used.
[0100] The content of the chiral agent in the polymerizable liquid
crystal composition is preferably 0.01 mol % to 200 mol %, and more
preferably 1 mol % to 30 mol %, of the amount of the polymerizable
liquid crystal compound.
[0101] --Cationic Initiator (Photocation Generating Agent)--
[0102] The photocation generating agent may be any compound as long
as it has an action of generating an acid by light irradiation and
initiating cationic polymerization of an oxetanyl group; however,
an onium salt is preferred. In this case, the counter anion may be
any of an organic anion and an inorganic anion. Examples of the
onium salt include an iodonium salt, a diazonium salt, and a
sulfonium salt; however, a sulfonium salt and an iodonium salt are
preferred. In consideration of thermal stability, a sulfonium salt
is more preferred. Regarding the photocation generating agent,
those described in paragraph [0053] of JP2008-127336A can be
utilized as appropriate.
[0103] The amount of addition of the photocation generating agent
may vary depending on the structure of the mesogenic group or the
spacer in the polymerizable liquid crystal compound, the oxetanyl
group equivalent, the conditions for orientation of liquid
crystals, and the like; however, conventionally, the amount of
addition is usually 100 ppm by mass to 20% by mass, preferably
1,000 ppm by mass to 10% by mass, more preferably 0.2% by mass to
7% by mass, and most preferably in the range of 0.5% by mass to 5%
by mass, with respect to the total mass of the monomers in the
liquid crystalline composition.
[0104] --Other Components--
[0105] A composition used in order to form a twisted liquid
crystalline phase may include, in addition to the liquid crystal
compound, the chiral agent, and the cationic initiator described
above, other components such as an orientation controlling agent
and an alignment aid. For all of them, known materials can be
utilized.
[0106] --Solvent--
[0107] Regarding the solvent of compositions for realizing a
twisted liquid crystalline phase and an isotropic phase, an organic
solvent is preferably used. Examples of the organic solvent include
an amide (for example, N,N-dimethylformamide), a sulfoxide (for
example, dimethyl sulfoxide), a heterocyclic compound (for example,
pyridine), a hydrocarbon (for example, benzene and hexane), an
alkyl halide (for example, chloroform and dichloromethane), an
ester (for example, methyl acetate and butyl acetate), a ketone
(for example, acetone, methyl ethyl ketone, and cyclohexanone), and
an ether (for example, tetrahydrofuran and 1,2-dimethoxyethane). An
alkyl halide and a ketone are preferred. Two or more kinds of
organic solvents may be used in combination.
[0108] <Formation of Depolarizing Layer>
[0109] A method for forming a depolarizing layer will be explained
with reference to the production process illustrated in FIG.
11.
[0110] <<Coating step>>
[0111] A polymerizable liquid crystal composition is evenly applied
on the surface of a support 10 (or an oriented film provided on a
support), and a coating film 20A is formed (S1).
[0112] Application of the polymerizable liquid crystal composition
can be carried out by converting the polymerizable liquid crystal
composition into a solution state using a solvent or into a liquid
material such as a molten liquid obtained by heating, and spreading
the solution or the liquid material by an appropriate method such
as a roll coating method, a gravure printing method, or a spin
coating method, or the like. Furthermore, the application can be
carried out by various methods such as a wire bar coating method,
an extrusion coating method, a direct gravure coating method, a
reverse gravure coating method, and a die coating method. A coating
film can also be formed by discharging a liquid crystal composition
through a nozzle using an inkjet apparatus.
[0113] <<Aging Step>>
[0114] The coating film 20A is maintained (aged) at a twisted
liquid crystalline phase formation temperature for a certain time
period, and the liquid crystal molecules are aligned into a twisted
phase (S2). The aging temperature and the aging time may be
determined according to the liquid crystal compound.
[0115] <<Ultraviolet (UV) Curing Step>>
[0116] After the aging step, ultraviolet curing is carried out in
order to fix the alignment state of the molecules of the liquid
crystal compound. In the ultraviolet curing step, a polymerization
reaction by means of a photocation polymerizable group (photocation
polymerization reaction) and a polymerization reaction by means of
a photoradical polymerizable group (photoradical polymerization
reaction) are carried out separately. According to the present
specification, the coating film obtained after the first
polymerization process between the two stages of polymerization in
the ultraviolet curing step is referred to as semi-fixed liquid
crystal film. The procedure of the curing step will be
described.
[0117] 1) Full-Face Exposure Step
[0118] The entire surface of the coating film 20B in a state of
being oriented in a twisted liquid crystalline phase is irradiated
with ultraviolet radiation at an exposure amount of 100 to 2,000
mJ/cm.sup.2 in air, and thereby the entire surface of the coating
film 20B is subjected to almost uniform exposure (S3). At this
time, mainly cationic polymerization proceeds as a result of the
action of the cationic polymerization initiator included in the
coating film 20B. Meanwhile, it is still acceptable that radical
polymerization has partially occurred. As a result of this
full-face exposure, a portion is crosslinked (partial curing) over
the entire surface, and thereby a semi-fixed liquid crystal film
20C in which the alignment state of the liquid crystal is
semi-fixed is obtained. The term "semi-fixed" refers to a state in
which the liquid crystal composition in the invention has lost
fluidity, and refers to a state prior to a heat treatment step. For
example, the term implies that only one side functional group of a
bifunctional liquid crystal is crosslinked, and thereby a polymeric
liquid crystalline state is achieved. In the case of a
polymerizable liquid crystal compound including a cationic
polymerizable group and a photoradical polymerizable group, the
term refers to a state in which one of the cationic polymerizable
group or the photoradical polymerizable group is selectively
crosslinked. In the present full-face exposure step, the term
refers to a state in which the cationic polymerizable group is
selectively crosslinked; however, it is still acceptable that
crosslinking by the photoradical polymerizable group has partially
occurred.
[0119] 2) Initiator Application Step
[0120] On the surface of the semi-fixed liquid crystal film 20C
described above, an initiator supply liquid including a
photoradical polymerization initiator is applied and dried.
[0121] 3) Mask Exposure Step
[0122] Subsequently, in a state of having a predetermined mask 40
disposed on the semi-fixed liquid crystal film 20C, the semi-fixed
liquid crystal film 20C is irradiated with ultraviolet radiation in
an exposure amount of 30 to 100 mJ/cm.sup.2 in air at room
temperature, through a predetermined mask 40 (S4). In the
predetermined mask 40, in order to obtain a first region and a
second region in a desired pattern, an opening part 42
corresponding to the first region and a non-opening part 44
corresponding to the second region have been formed. Thereby,
patterned exposure is achieved, by which a region exposed to the
mask opening part 42 in the semi-fixed liquid crystal film 20C is
exposed to light, and the part covered with the mask non-opening
part 44 is not exposed to light. At this time, in the exposed
region, photoradical polymerization induced by the action of the
photoradical polymerization initiator proceeds.
[0123] <<Heat Treatment Step>>
[0124] The entire substrate including the semi-fixed liquid crystal
film 20D and the support as obtained after the exposure step is
heated for a predetermined time period at an isotropic phase
formation temperature (temperature higher than or equal to the
temperature for phase transition into an isotropic phase) of the
liquid crystal compound (S5).
[0125] By means of this heat treatment, the liquid crystal forms an
isotropic phase in the region that has not been subjected to mask
exposure. The isotropic phase may be further stabilized by
performing post-exposure after the heat treatment.
[0126] Through the above-described processes, a depolarizing layer
20 in which the first region 21 formed from a twisted liquid
crystalline phase and the second region 22 formed from an isotropic
phase are formed into a pattern, can be obtained (S6).
[0127] In the above description, the case in which a cationic
polymerizable group of a polymerizable liquid crystal compound
having a cationic polymerizable group and a photoradical
polymerizable group is polymerized first, and then the photoradical
polymerizable group is polymerized, has been described; however, a
depolarizing layer having a similar twisted phase and a similar
isotropic phase can be formed also by the procedure of polymerizing
the photoradical polymerizable group first and then polymerizing
the cationic polymerizable group. In this case, regarding the
polymerizable liquid crystal composition described above, it is
desirable to use a liquid crystal composition including a
photoradical polymerization initiator instead of a cationic
polymerization initiator. Then, the photoradical polymerization
initiator application step is not needed, and before cationic
polymerization is carried out separately, a cationic initiator
application step may be provided.
[0128] Next, elements other than the depolarizing layer among the
elements that constitute the depolarizing film will be
explained.
[0129] [Support]
[0130] The depolarizing film may include a support, and the support
is preferably a transparent support. Examples include a film of a
polyacrylic resin such as polymethyl methacrylate; a film of a
cellulose-based resin such as cellulose triacetate; and a
cycloolefin polymer-based film [for example, trade name "ARTON"
manufactured by JSR Corporation, trade name "ZEONOR", manufactured
by Zeon Corporation]. The support is not limited to a flexible film
and may be a non-flexible substrate such as a glass substrate.
[0131] The depolarizing film in the invention may be used while
being supported by the support used at the time of forming a film.
Alternatively, the support used at the time of forming a film may
be used as a temporary support, the depolarizing film may be
transferred onto another support, and the depolarizing film may be
used after the temporary support is detached.
[0132] [Oriented Film]
[0133] On the support for forming a liquid crystal layer, an
oriented film may be provided. The oriented film can be provided by
means of a rubbing treatment of an organic compound (preferably, a
polymer), oblique vapor deposition of an inorganic compound,
formation of a layer having microgrooves, and the like.
Furthermore, an oriented film acquiring a function of orientation
by means of impartation of an electric field, impartation of a
magnetic field, or light irradiation is also known. It is
preferable that the oriented film is formed by subjecting the
surface of a film of a polymer to a rubbing treatment. In the case
of using a depolarizing film after detaching from the support used
at the time of film forming, it is preferable that the oriented
film is detached together with the support.
[0134] In the case of using a support made of a resin, depending on
the polymer type, the support can be made to function as an
oriented film, even without providing an oriented film, by
subjecting the support to a direct alignment treatment (for
example, rubbing treatment). An example of such a support may be
PET (polyethylene terephthalate).
[0135] [.lamda./4 Plate]
[0136] As described previously, a broadband .lamda./4 plate is
preferred, and a commercially available .lamda./4 plate can be used
as appropriate.
[0137] [Adhesive Layer (Pressure-Sensitive Adhesive Layer)]
[0138] According to the present specification, "adhesion" is used
as a concept also including "pressure-sensitive adhesion".
[0139] The depolarizing layer 20 and the .lamda./4 plate 30 may be
laminated with an adhesive layer interposed therebetween.
[0140] Examples of a pressure-sensitive adhesive used for the
adhesive layer include resins such as a polyester-based resin, an
epoxy-based resin, a polyurethane-based resin, a silicone-based
resin, and an acrylic resin. These may be used alone, or two or
more kinds thereof may be used as mixtures. Particularly, an
acrylic resin is preferred from the viewpoint that the resin has
excellent reliability such as water resistance, heat resistance,
and light resistance, has satisfactory adhesive force and
transparency, and can have the refractive index easily adjusted so
as to suit liquid crystal displays.
EXAMPLES
[0141] Hereinafter, Examples and Comparative Examples of the
depolarizing film in the invention will be described.
[0142] First, the production of various compositions used for the
production of the depolarizing films of Examples and Comparative
Examples will be described.
[0143] (Production of Oriented Film Composition B)
<Synthesis of Polymer for Oriented Film Composition>
[0144] Into a reaction vessel equipped with a stirrer, a
thermometer, a dropping funnel, and a reflux cooling tube, 100
parts by mass of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 500
parts by mass of methyl isobutyl ketone, and 10 parts by mass of
triethylamine were introduced, and the mixture was mixed at room
temperature.
[0145] Next, 100 parts by mass of deionized water was added
dropwise from the dropping funnel to the solution in the reaction
vessel over 30 minutes, and then a solution thus obtained was
caused to react for 6 hours at 80.degree. C. while being mixed
under reflux. After completion of the reaction, an organic phase
was extracted from the solution, and the organic phase was washed
until the water that had been used to wash the organic phase became
neutral with a 0.2 mass% aqueous solution of ammonium nitrate.
Subsequently, the solvent and water were distilled off under
reduced pressure, and thereby an epoxy group-containing
polyorganosiloxane was obtained as a consistent transparent
liquid.
[0146] This epoxy group-containing polyorganosiloxane was subjected
to a .sup.1H-NMR (Nuclear Magnetic Resonance) analysis, and a peak
based on an oxilanyl group was obtained at a theoretical intensity
at a chemical shift (.delta.)=near 3.2 ppm. Thus, it was confirmed
that side reactions of epoxy groups did not occur during the
reaction. The weight average molecular weight M.sub.w of this epoxy
group-containing polyorganosiloxane was 2,200, and the epoxy
equivalent was 186 g/mol.
[0147] Next, into a 100-mL three-necked flask, 10.1 parts by mass
of the epoxy group-containing polyorganosiloxane obtained as
described above, 0.5 parts by mass of an acrylic group-containing
carboxylic acid (Toagosei Co., Ltd., trade name "ARONIX M-5300",
.omega.-carboxypolycaprolactone acrylate (degree of polymerization
n.apprxeq.2)), 20 parts by mass of butyl acetate, 1.5 parts by mass
of a cinnamic acid derivative obtained by the method of Synthesis
Example 1 of JP2015-26050A, and 0.3 parts by mass of
tetrabutylammonium bromide were introduced, and a reaction solution
thus obtained was stirred for 12 hours at 90.degree. C.
[0148] After completion of the reaction, the reaction solution was
diluted with an equal amount (mass) of butyl acetate, and the
dilution was washed with water three times.
[0149] An operation of concentrating the solution thus obtained and
diluting the concentration with butyl acetate was repeated two
times, and finally, a solution including a polyorganosiloxane
(polymer) having a photo-alignable group was obtained. The weight
average molecular weight M.sub.w of this polymer was 9,000. As a
result of a .sup.1H-NMR analysis, the proportion of the component
having a cinnamate group in the polymer was 23.7% by mass.
[0150] <Production of Oriented Film Composition B>
[0151] Butyl acetate was used as a solvent, and the polymer
produced previously and the following compound D1 and compound D2
were added thereto in the following amounts. Thus, oriented film
composition B was produced.
TABLE-US-00001 Oriented film composition B (parts by mass) Butyl
acetate 100 Polymer for oriented film composition 4.35 Compound D1
0.48 Compound D2 1.15 ##STR00006## D1 ##STR00007## D2
[0152] (Production of Polymerizable Liquid Crystal Composition
LC-2)
[0153] After the following composition was produced, the
composition was filtered through a filter made of polypropylene and
having a pore size of 0.2 .mu.m, and the resultant was used as
polymerizable liquid crystal composition LC-2.
[0154] A rod-shaped liquid crystal (LC-1-1) was synthesized based
on the method described in JP2004-12382A. The rod-shaped liquid
crystal (LC-1-1) is a liquid crystal compound having two reactive
groups, and one of the two reactive groups is an acryl group, which
is a radical reactive group, while the other is an oxetane group,
which is a cationic reactive group. A horizontal alignment agent
(LC-1-2) was synthesized according to the method described in
Tetrahedron Lett., Vol. 43, page 6793 (202).
TABLE-US-00002 Polymerizable liquid crystal composition LC-2 (parts
by mass) Rod-shaped liquid crystal (LC-1-1) 19.57 Horizontal
alignment agent (LC-1-2) 0.01 Chiral agent having the following
structure 0.035 Cationic monomer (OXT-121, manufactured by Toagosei
Co., Ltd.) 0.98 Cationic polymerization initiator 0.4 (Curacure
UV16974, manufactured by Dow Chemical Company) Polymerization
controlling agent 0.02 (IRGANOX 1076, manufactured by BASF SE)
Methyl ethyl ketone 80.0 ##STR00008## (LC-1-1) ##STR00009##
(LC-1-2) Chiral agent ##STR00010##
[0155] (Production of Initiator Supply Liquid AD-1)
[0156] The following composition was produced, and then the
composition was filtered through a filter made of polypropylene and
having a pore size of 0.2 .mu.m. Thus, the resultant was used as an
initiator supply liquid AD-1.
TABLE-US-00003 Initiator supply liquid AD-1 (parts by mass)
Photoradical polymerization initiator (2-trichloromethyl-5- 0.12
(p-styrylstyryl)-1,3,4-oxadiazole) Hydroquinone monomethyl ether
0.002 MEGAFAC F-176PF (manufactured by DIC Corporation) 0.05
Propylene glycol monomethyl ether acetate 34.80 Methyl ethyl ketone
50.538 Methanol 1.61
Example 1
[0157] The production of the depolarizing film of Example 1 was
carried out by the following procedure.
[0158] <Formation of Oriented Film>
[0159] The oriented film composition B produced as described above
was uniformly applied on a glass substrate using a slit coater and
then was dried in an oven at 100.degree. C. for 2 minutes. Thus, an
oriented film-attached glass substrate having a film thickness of
0.5 .mu.m was obtained. This oriented film was subjected to a
rubbing treatment in a direction parallel to the direction of
application.
[0160] <Formation of Depolarizing Layer>
[0161] The polymerizable liquid crystal composition LC-2 was
applied on the rubbing-treated surface of the oriented film, and a
coating film was formed (coating step).
[0162] Next, the coating film was heated and aged for 60 seconds at
a film surface temperature of 80.degree. C., and the coating film
was oriented in a twisted liquid crystalline phase (aging
step).
[0163] Thereafter, immediately, the entire surface of the coating
film was irradiated with ultraviolet radiation at a dose of 500
mJ/cm.sup.2 using an air-cooled metal halide lamp (manufactured by
Eye Graphics Co., Ltd.) in air at a film surface temperature of
70.degree. C., and full-face exposure was carried out (UV curing
step: full-face exposure step). Photocationic polymerization was
carried out, and the alignment state was semi-fixed. Thereby, a
semi-fixed liquid crystal film was formed.
[0164] On the semi-fixed liquid crystal film obtained in this
manner, the initiator supply liquid AD-1 produced as described
above was applied and dried at 80.degree. C. for 60 seconds (UV
curing step: initiator application step).
[0165] Subsequently, the semi-fixed liquid crystal film was exposed
by irradiating the film with ultraviolet radiation through a
predetermined mask in an exposure amount of 50 mJ/cm.sup.2 in air
at 25.degree. C. using a PLA-501F exposure machine (ultrahigh
pressure mercury lamp) manufactured by Canon, Inc. (UV curing step:
mask exposure step), and photoradical polymerization in an exposed
region (mask opening region) was carried out. The predetermined
mask was such that opening parts and non-opening parts were
disposed alternately at a period of 10 .mu.m, that is, opening
parts having a width of 5 .mu.m and non-opening parts having a
width of 5 .mu.m were alternately formed into stripe shapes.
[0166] Subsequently, the entire substrate including the
mask-exposed semi-fixed liquid crystal film was fired in an oven at
200.degree. C. for 30 minutes (heat treatment step), and a
depolarizing layer having a first region and a second region was
obtained.
[0167] In this manner, a depolarizing film of Example 1 was
produced.
[0168] It was confirmed that the UV-irradiated first region, which
corresponded to the opening region of the mask, was a region having
the liquid crystal layer twisted by 90.degree. and having a
function of achieving 90.degree. optical rotation, while the second
region that was not irradiated with UV, which corresponded to the
non-opening region of the mask, lost birefringence of the liquid
crystal layer and became an optically isotropic region.
[0169] The depolarizing layer thus completed was cut to expose a
cross-section, and the film thickness was measured from a SEM
image. Measurement was carried out at a plurality of sites such as
three or more sites, and the average value was designated as the
film thickness of the depolarizing layer. The film thickness of the
depolarizing layer thus obtained was 3 .mu.m.
Example 2
[0170] The depolarizing film of Example 1 was bonded together with
a .lamda./4 plate that had been prepared separately, and the
resultant was used as a depolarizing film of Example 2.
[0171] As the .lamda./4 plate, a broadband wavelength plate,
B-RETAX-1/4X-30, of Luceo Co., Ltd. was used. The in-plane
retardation Re (X) and the thickness-direction retardation Rth (X)
at a wavelength X of the film of the broadband wavelength plate
were Re (550) =125 nm and Rth (550) =1 nm, respectively. The
depolarizing film of Example 1 and the .lamda./4 plate were bonded
together using a pressure-sensitive adhesive (SK-2057, manufactured
by Soken Chemical & Engineering Co., Ltd.).
Comparative Example 1
[0172] A depolarizing film in which a first region formed from a
.lamda./2 plate and a second region formed from an optically
isotropic member were alternately disposed was produced by
referring to JP2006-047421A.
[0173] [Evaluation]
[0174] For the various depolarizing films, linearly polarized light
or circularly polarized light was made incident, and the degree of
depolarization was measured.
[0175] (Method for Measuring Degree of Depolarization)
[0176] The degree of depolarization was measured using an
elliptical polarization analyzer KOBRA-WPR of Oji Scientific
Instruments Co., Ltd. and using a PR software program for
elliptical polarization analysis and a TR software program for
transmittance measurement of the same company.
[0177] For the depolarizing film of each example, a sample for
measurement that measured 20 mm on each side was produced and
submitted to measurement. The samples of Example 1 and Comparative
Example 1 were irradiated with an incident ray as linearly
polarized light in a 5-mm.PHI. (diameter) circular region, and the
degree of depolarization was measured. Subsequently, in the
apparatus, the polarizing axis of the incident ray was shifted by
45.degree. each time, the initial measurement was set at 0.degree.
(P.sub.0), and the angle of the polarizing axis of the incident ray
was changed to 45.degree. (P.sub.45), 90.degree. (P.sub.90), and
135.degree. (P.sub.135). The degree of depolarization of each
depolarizing film was measured. Furthermore, for the sample of
Example 2, circularly polarized light was used as an incident ray,
and the degree of depolarization was measured. At this time,
measurement was carried out respectively for left-handed circularly
polarized light and right-handed circularly polarized light.
[0178] The wavelength of the incident ray was set at 550 nm.
Meanwhile, the same measurement was carried out even at wavelengths
other than 550 nm (450 nm and 630 nm), and the results were
approximately the same as that for 550 nm. Here, the results
obtained at 550 nm will be shown as representative results.
[0179] (Evaluation Criteria)
[0180] The degree of depolarization thus measured was evaluated
according to the following criteria.
[0181] A: higher than 95%
[0182] B: higher than 90% and 95% or lower
[0183] C: higher than 50% and 90% or lower
[0184] D: 50% or lower
[0185] The configurations and evaluation results of the various
examples are shown together in Table 1.
TABLE-US-00004 TABLE 1 COMPAR- ATIVE EXAM- EXAM- EXAM- PLE 1 PLE 2
PLE 1 Config- Depo- First Twisted Twisted .lamda./2 uration
larizing region liquid liquid plate of depo- layer crystalline
crystalline larizing phase phase film Second Isotropic Isotropic
Transparent region phase phase material (optical isotropy)
.lamda./4 plate Absent Present Absent Degree Incident ray: linearly
A -- D of depo- polarized light lariza- Polarizing axis P.sub.0
tion Incident ray: linearly A -- D polarized light Polarizing axis
P.sub.90 Incident ray: linearly A -- A polarized light Polarizing
axis P.sub.45 Incident ray: linearly A -- A polarized light
Polarizing axis P.sub.135 Incident ray: circularly -- A --
polarized light Left-handed circularly polarized light P.sub.L
Incident ray: circularly -- A -- polarized light Right-handed
circularly polarized light P.sub.R
[0186] As shown in Table 1, the depolarizing film of Example 1
could realize satisfactory depolarization irrespective of the angle
of the polarizing axis in a case in which the incident ray was
linearly polarized light. The depolarizing film of Example 2 could
realize satisfactory depolarization in a case in which the incident
ray was circularly polarized light. Since Comparative Example 1
used a .lamda./2 plate, satisfactory depolarization could be
realized for linearly polarized light having a polarizing axis
inclined by 45.degree. or 135.degree. with respect to the slow axis
of the .lamda./2 plate; however, with polarizing axes at different
inclinations, the effect of depolarization was hardly obtained.
From the results of Examples 1 and 2, it is speculated that in a
case in which a depolarizing member is constructed by superposing
these depolarizing films of Examples 1 and 2, satisfactory
depolarization can be realized for both linearly polarized light
and circularly polarized light.
EXPLANATION OF REFERENCES
[0187] 1, 2: depolarizing film
[0188] 1a, 2a: one surface of depolarizing film
[0189] 1b, 2b: the other surface of depolarizing film
[0190] 5: depolarizing member
[0191] 5a: one surface of depolarizing member
[0192] 5b: the other surface of depolarizing member
[0193] 10: support
[0194] 20, 120, 220: depolarizing layer
[0195] 20A: coating film
[0196] 20B: coating film oriented in twisted liquid crystalline
phase
[0197] 20C: semi-fixed liquid crystal film
[0198] 21, 121, 221: first region
[0199] 22, 122, 222: second region
[0200] 30: .lamda./4 plate
[0201] 40: mask
[0202] 42: opening
[0203] 44: non-opening
* * * * *